Most modern diesel engines, particularly diesel engines for large tractor-trailer trucks, use fuel injectors to deliver a desired fuel charge to an engine cylinder. The fuel injector is a nozzle which injects fuel, atomized by forcibly pumping fuel through the nozzle at high pressure, directly into the combustion chamber of each cylinder. A fuel injector, particularly a fuel injector for use with a diesel engine, is required to accurately discharge a quantity of fuel into a combustion chamber of an internal combustion engine over a wide range of engine operating conditions.
Fuel is injected into the combustion chamber during the final stage of compression. The high degree of compression heats the air such that the heat initiates combustion of the fuel when the fuel is injected into the chamber. The fuel injector ensures that fuel is injected in fine droplets to allow for even distribution, which enhances efficiency of the combustion process and results in improved engine performance.
The start of injection (SOI) is determined by the fuel injection timing of the fuel system, often controlled by an engine control unit (ECU). SOI timing is an important factor in lowering emissions and improving engine efficiency. Timing of the SOI is measured in degrees of the crank angle of the piston before top dead center (BTDC), which is the highest position the piston reaches in the cylinder. The ECU receives input on engine operating conditions such as the engine speed, indicated torque, intake manifold pressure, oxygen concentration, and fuel temperature. Based on the engine operating conditions, the ECU determines an optimal SOI time to maximize power and efficiency while minimizing emissions.
In many engines, exhaust gas recirculation (EGR) rates are decreased during transient operation to avoid engine misfire, usually due to a decreased air to fuel ratio as a result of turbocharger delay. However, because stricter emission standards do not allow for such decreased EGR rates, attempts are made to shift injection timing to avoid engine misfire. Under-advanced SOI timing, or delaying start of injection, causes incomplete combustion, produces unburned hydrocarbons and poor fuel efficiency due to late combustion phasing. Current technology typically advances injection timing significantly during transient operation causing engine misfire. Overly-advanced SOIs, or injecting before the piston reaches TDC, can result in higher in-cylinder pressure and temperature, and higher efficiency, but also results in elevated engine noise and excess nitrous oxide (NOx) production.
The present inventors have recognized that SOI timing can be derived from correlations of ignition delay and information based on steady state engine operating conditions which are readily achieved in an experimental setting. Because the engine is often subject to conditions when ideal correlations cannot be maintained, timing SOI during transient operating conditions based on an ignition delay correlation can optimize engine performance.
The present inventors have recognized the need for a method of improving injection timing control to decrease engine misfire, and to avoid excessively advanced combustion.
The present inventors have recognized the need for an engine management system that enables the operation of an engine with high levels of EGR and late combustion timings while containing misfiring events.
The present inventors have recognized that SOI compensation based on ignition delay correlation can contain combustion phasing under transient operating conditions.